The delivery of radio frequency (RF) energy to target regions of solid tissue is known for a variety of purposes of particular interest to the present inventions. In one particular application, RF energy may be delivered to diseased regions (e.g., tumors) in target tissue for the purpose of tissue necrosis. RF ablation of tumors is currently performed within one of two core technologies.
The first technology uses a single needle electrode, which when attached to a RF generator, emits RF energy from the exposed, uninsulated portion of the electrode. This energy translates into ion agitation, which is converted into heat and induces cellular death via coagulation necrosis. In theory, RF ablation can be used to sculpt precisely the volume of necrosis to match the extent of the tumor. By varying the power output and the type of electrical waveform, it is possible to control the extent of heating, and thus, the resulting ablation. The diameter of tissue coagulation from a single electrode, however, has been limited by heat dispersion. As a result, multiple probe insertions have been required to treat all but the smallest lesions. This considerably increases treatment duration and requires significant skill for meticulous precision of probe placement. Increasing generator output has been unsuccessful for increasing lesion diameter, because an increased wattage is associated with a local increase of temperature to more than 100° C., which induces tissue vaporization and charring. This then increases local tissue impedance, limiting RF deposition, and therefore heat diffusion and associated coagulation necrosis.
The second technology utilizes multiple needle electrodes, which have been designed for the treatment and necrosis of tumors in the liver and other solid tissues. PCT application WO 96/29946 and U.S. Pat. No. 6,379,353 disclose such probes. In U.S. Pat. No. 6,379,353, a probe system comprises a cannula having a needle electrode array reciprocatably mounted therein. The individual electrodes within the array have spring memory, so that they assume a radially outward, arcuate configuration as they are advanced distally from the cannula. In general, a multiple electrode array creates a larger ablation area than that created by a single needle electrode. Some medical personnel, however, still prefer to use single needle electrodes, either because they feel more comfortable with single needle electrodes, find it difficult to accurately deploy multiple electrode arrays, and/or are concerned that one or more of the multiple needle electrodes, which are mounted to the probe with one connection, may break off in the tumor.
There, thus, remains a need to provide a single electrode ablation probe that can create larger ablation area.